For the second time in a year, my car has built up a layer of bonded contaminants on the rear bumper and trunk lid. They come off with clay, but aren't building up on the rest of the car. Also, this is where dust / dirt accumulate first after washing.

So...am wondering if there's some odd swirling / turbulence at the rear that causes this? Especially if the top is down (which it usually is)? Anyone else experiencing this, and/or has an idea on how to reduce it?

do you have any type of protection on the car? like a wax or sealant? sounds like that will fix your problem but not entirely fix it. the rear will always get dirty after a wash the fastest out of all the parts on the car. it's just how it is but when you have some type of protection there will be less contamination and it will easier to wash off

The rear of this car sees more contaminant build up then any other part on the car..i use Collinite 845 on these areas...its a boat wax thats is much more suited to protect the rear bumper and trunk lid

For the second time in a year, my car has built up a layer of bonded contaminants on the rear number and trunk lid. They come off with clay, but aren't building up on the rest of the car. Also, this is where dust / dirt accumulate first after washing.

So...am wondering if there's some odd swirling / turbulence at the rear that causes this? Especially if the top is down (which it usually is)? Anyone else experiencing this, and/or has an idea on how to reduce it?

Cheers

Rear of any vehicle is always the dirtiest. This is down to basic aerodynamics. Any object moving fast enough will create an area of low pressure behind it, therefore "sucking" in objects/particles that are light enough.

Coupe here and yes, the backed gets hammered. I track and 4-season DD my car and it gets 1-2 full details a year with the majority of the time spent on the back end. Best advice is lay down a good sealant and maintain with wax on top to prolong protection.

no offence to the zaino users, but replace zaino with opti coat, or the professionally installed opti guard.

the contaminants will come off easier and without clay.

Also with Opti coat, you could use ironx x instead of clay to wash the contaminants off instead of claying all the time (which will eventually lead to polishing).

also, ive read alot about zaino attracting dust and dirt...like an electrostatic charge that acts like a dirt magnet.

as for the swirls, proper wash techinique after they are removed. BMW clear is one of the hardest being a ceramic clear. id look to Menzerna PF 2500 for a one step, or FG 4000 for a heavier cut, but a polish like finish. they should take care of the swirls.

the problem with a dealership prep, even on a used car, is that they often use glazes...they are high shine products which contain fillers. the car looks great fora couple of weeks until the fillers wear off, then you see the real condition of the paint. the only way to remove the swirls is to abrade them out with polish or compound. then get a tough layer of protection on the car.